*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
.aa{
    left:50%;
    top:50%;
    transform:translate(-50%,-50%);
    position: fixed;
    font-size:0 ;
}
.a{
    width: 20px;
    height: 20px;
    background: red;
    border-radius: 50%;
    display:inline-block;
    animation-name: move;
    animation-iteration-count: infinite;
    animation-timing-function: linear;
    animation-duration:1s;
    animation-direction: alternate;
    margin-right: 20px;
}
@keyframes move{
    0%{
        transform: scale(1.5);
    }
    100%{
        transform: scale(0);
    }
}
.a2{
    animation-delay:0.3s ;
}
.a3{
    animation-delay:0.6s ;
}